1. Field of the Invention
This invention relates to a means of actuating a brake system in a towed vehicle such as, but not restricted to, an automobile or truck, by means of utilizing the existing brake system of the towed vehicle in conjunction with a towing vehicle's brake system. The invention not only permits service brake actuation of the towed vehicle while it is towed, but also provides for emergency actuation of the vehicle brakes in the event said towed vehicle breaks loose from being towed.
2. Background Information
In some states within the United States and at least one province in Canada require that an automobile, when towed, must have its brake system actuated as the towing vehicle brakes are actuated. Also, if the automobile being towed breaks loose from the towing vehicle, the brakes automatically actuate. There are limitations to braking systems currently used.
There is a BRAKEMASTER (TM) proportionate braking system by Roadmaster, Inc., a firm located at 5602 N.E. Skyport Way, Portland, Oreg. 907218 which consists of an air cylinder rigged up to actuate a towed vehicle's brake pedal. This brake system is in use in conjunction with motor homes towing vehicles, especially light cars. The air cylinder is actuated from air tapped off the air or air over hydraulic brake system of the motor homes that have air or air over hydraulic brake systems. For motor homes that do not have an air system, a compressor is required to be added. A problem with an air system is moisture in the air, especially in wintertime. A problem with an air cylinder actuating a towed vehicle's brake pedal is that, while a vehicle is being towed, the vehicle's vacuum power boost system is off. This means excessive brake pedal force is required to compensate for the lack of vacuum boost that would be available if the towed vehicle was being driven instead of towed. This excessive brake pedal force, as it is repeated enough times, wears out the mechanical linkages, connections, and structure of the brake pedal and the surrounding structure of the vehicle to which the brake pedal is mounted. Typically, this is that surrounding structure is the firewall of the vehicle, which wasn't designed to withstand repetitive excessive force applications on the brake pedal attached to the firewall.
On all hydraulic brake systems, tapping into the towed vehicle's brake system could void the brake warranty of the towed vehicle.
There is a TOAD STOP (TM) VAC-BRAKE (TM) which uses vacuum from an engine of a towing vehicle in conjunction with a double acting vacuum cylinder with two three-way electric solenoid operated vacuum valves to pull on a brake cable which pulls on an attachment to the towed vehicle's brake pedal as the towing vehicle brake pedal is actuated. As vacuum is not available from a diesel engine, the applicability of this system is restricted to towing vehicles with gasoline powered engines. Also there are problems resulting from cable stretch, cable fraying, and fitting connections to the cable. Also, in this system, the vacuum is used to retract the vacuum cylinder's piston to pull on the brake cable. Retracting a vacuum cylinder's piston to exert force, or move a load, is less efficient than extending a vacuum cylinder's piston to exert a force, or move a load. For example, a one and a half inch diameter vacuum cylinder, with a single one half inch rod, which is a typical cylinder for such an application, is 11% less efficient in retracting a load, as opposed to being used to extend a load. In the event of a towed vehicle breaking loose from a towing vehicle, the system actuates automatically. A limitation to this approach is that for many smaller cars, there is insufficient space under the hood of the car for the vacuum cylinder. Also, the brake cable comes through the firewall of the towed vehicle to a bracket attached to the towed vehicle's brake pedal. When a person wants to drive said towed vehicle, there is a problem of what to do with the pedal bracket and cable. A loose cable end and the bracket on the floor of the vehicle is apt to get in the way of a driver's foot while the driver is trying to actuate a pedal. Also, to ensure sufficient vacuum for stopping the towed vehicle in the event of a breakway condition, an optional vacuum reservoir is available that usually will not fit in the engine compartment of small cars, such as a SATURN (TM). The TOAD STOP (TM) VAC-BRAKE (TM) uses vacuum derived from a towing vehicle engine creating the possibility of contamination entering the towing vehicle engine which could cause engine wear and failure.
Both of the above systems rely on hoses from the towing vehicle to the towed vehicle which involves a hose the length of the towing vehicle as well as two quick disconnects in the hoses between the vehicles. The hose between the two vehicles runs a risk of hose damage from road hazards. Three quick disconnects are required. For vacuum systems, dirt can enter the equipment on the towing vehicle. For hydraulic hoses, leakage which means a loss of fluid can result. For air systems, air pressure can be lost, which can cause a serious problem with the towing vehicle brake system.
Existing systems tend to use a three way air or vacuum valve for cylinder rod actuation in a given direction and rely on brake system return springs for return of the pedal with attachments. This can cause brake drag in some circumstances. As will be seen from the subsequent description of the preferred embodiment of the present invention, the present invention overcomes these and other shortcomings of the prior art.